The purpose of this investigation will be to determine the environmental and behavioral factors which initiate or maintian changes in impulse activity of norepinephrine-containing locus coeruleus (LC-NE) neurons. Discharge rates and patterns of these neurons will be recorded extracellularly in anesthetized as well as unanesthetized, behaviorally active, rats and squirrel monkeys. Preliminary data from both species are presented which demonstrate that, in the unanesthetized animal, LC-NE neurons: 1) discharge more rapidly during waking than during drowsiness or sleep, 2) exhibit bursts of action potentials in response to both simple and complex auditory, visual, and somesthetic stimuli, 3) may exhibit response magnitude decreases during repeated presentations of such stimuli, and 4) do not alter their activity consistently with the occurrence of any specific motor act. Experiments are proposed to systematize, quantify, and extend these observations. These analyses will measure the relative potencies of the following variables in determining LC-NE discharge activity: 1) electrographically defined sleep-waking stages, b) systematically repeated, qualitatively distinct sensory stimuli, c) topographical organization within LC, and d) level and type of anesthesia. These data will provide crucial evidence concerning the physiological function of these neurochemically characterize neurons whose post-synaptic influences are anatomically extensive and unusually well characterized.